Manufacture of rubber-bonded abrasive articles



UNITED STATES PATENT OFFICE MANUFACTURE OF RUBBER-BONDED ABBASIVE ARTICLES Royce J. Noble, Maiden, Masa, assignor to Reveatex Corporation, Melrose, Mala, a corporation of Massachusetts No Drawing. Application October 5, 1935, Serial No. 43,718

10 Claims. (Cl. 51278) This invention relates to the manufacture of oughly envelop the abrasive particles or develop rubber-bonded abrasive articles of the character sufficiently strong bonding aiilnity for the grain of grinding wheels. It involves, generally speaksurfaces even during vulcanization. ing, the mixing of abrasive grain such as car- 'The method of the present invention permits borundum, .corundum, alundum, or the like, with of the ready realization of substantially uniform 5 a vuicanizable rubber composition in granular mixture of abrasive grain and rubber in inexor pulverulent condition, the molding of the mixpensive mixing equipment with a minimum exture into an abrasive article of the desired shape, penditure of power and the preservation of the and the vulcanization of the molded article. particle size of the grain in the mixture. Not

According to one method of making abrasive only does my method require no rubber solvents, articles, the abrasive grain is mixed with rubber, but it leads to an abrasive article wherein the sulphur, and other rubber-compounding agents valuable quality of substantial homogeneity is on a rubber null. The mixture is then sheeted combined with tenacious bonding of the abrasive into the desired thickness, cut or dried out into pa i es by Such am unt 0! ru be d. if d such articles as grinding wheels, and the articles other bonding agent, as to ensure therein the vulcanized. The operation of repeatedly passing r quired abrading eiiectiveness.

the mixture of rubber and abrasive grain through In carrying out my method, the abrasive grain the nip of the mixing rolls of the mill is not only is mixed with substantially unvulcanized rubber wearing to the rolls but causes th grain to be in pulverulent condition in the presence of vulcrushed to such an extent that its average canizing ingredients and the mixture is molded m particle size is much lower than that of the origiand vulcanized under heat and pressure into an nai grain. This is a serious disadvantage when abrasive article of the desired shape, for instance, it is desired to produce abrasive articles with a grinding wheel. In order that the finished grain of predetermined comparatively large article possess appropriate strength, it is imparticle size. Again, there are limits to the portant that the pulverulent rubber be virgin, amount of grain that can be mixed with rubber that is, not previously vulcanized, although it is on a rubber mill, in consequence of which the possible to add thereto more or less ground reratio of rubber to grain may be greater than that claimed rubber or ground ebonite, depending upon leading to a finished article of the desired abradthe qualities sought in the finished article. The

ing effectiveness. vulcanizing ingredients employed may include 30 Another method of making abrasive articles Sulphur, nc Oxi e, a d vulcanization (B mconsists in dissolving or swelling rubber with any tor; and. if desired, pigments and fillers may be one of the usual volatile rubber solvents, such as P e in th m xtur Su j t to moldingnaphtha, mixing the grain with the resulting The abrasive grain may be of a natural or synrubber solution or cement, forming the mixture thetic character and be composed of various 35 into an article of the desired shape, and drying sized pa 'flc de d. it y be Preferable 0 and vulcanizing the article. Not only does this employ a mixture of rai s o two or mo e dismethod present a fire hazard and entail the loss tinctly d fl'e t a e Particle $1188 80 88 in of expensive solvent, but the last traces of 501- mi imi e Spacing betw Particles and e y 4o vent must be removed from the finished abrasive increase the density 01' he fini h d ilrl l l 40 article in order to avoid such defects as soft spots In some instances. I have found it distinctly and pockets such as are especially objectionable six-able to coat the abrasive granules with a in grinding wheels. primary bondfrg agent in the form of a solu- In still another method, the abrasive grain is tion which facilitates the disseminationoi the mixed with rubber latex compositions containing rubber powder throughout the grain. Such a r sulphur, fillers, and other rubber-compounding bonding agent is preferably one which not only agents and the mixture then formed into the dehas strong bonding aillnity for both the grain sired abrasive articles in much the same way as and the rubber but is capable of setting or hardwhen rubber cement is used. While rubber latex ening to a tough condit n under uch heat and P rm 1 h esi d mixing with low power pressure as may be employed in the vulcaniza- 50 consumption and no reduction in grain size, it is tion of the rubber. There are various polymerizdiilicult to realize the desired strong bond beable resins which answer the purpose of a primary tween the rubber and the grain surfaces. It apbonding agent, for instance, the phenolic resins, pears that the rubber deposited from latex, as by the vinyl resins, etc. While synthetic resins, es-

5 drying the latex-grain mixture. does not thorpecially the phenolic resins. are preferred, other bonding agents, such as hemoglobin or equivalent proteinous substance, may serve the function of a primary bonding agent, since they effect a strong bond between the rubber and the grain and tend to acquire a tough condition under heat and pressure.

Once the abrasive grain has been coated with a solution of the primary bonding agent, it is then mixed with the pulverulent rubber in the presence of vulcanizing ingredients, the mixture molded into an article of the desired shape, and the article dried to eliminate such solvent vehicle as has been introduced into the article along with the primary bonding agent. I prefer to use primary bonding agent in an amount by weight not greater than about 5% of the abrasive grain, in which case, the drying period for the initially molded article, assuming that it is a grinding wheel, will be about a to 6 hours, depending upon the thickness of the wheel and the amount and kind of solvent employed for the primary bonding agent. The dried molded article is then remolded under heat and substantial pressure so as to cause the rubber particles to unitestrongly and thus to bond the abrasive particles together while vulcanization is taking place.

One procedure embodying my invention and including the initial coating of the abrasive granules may be performed substantially as follows. To 100 parts of suitable abrasive grain, such as that hereinbefore mentioned is added parts of a 58% solution of phenolic resin capable of polymerizing further to a tough condition under heat. The solution and grain may be placed in a rotary drum and tumbled until the surfaces of the grains are uniformly wetted or coated with the solution. To the wetted grain is then added 10 to parts of a pulverulent rubber composition containing rubber and sulphur in the ratio of 100 parts of rubber to 40 parts of sulphur and containing a relatively small amount of a suitable accelerator of vulcanization. This mixture is stirred or'tumbled until the rubber powder is substantially uniformly disseminated throughout the mass of wet abrasive grains, whereupon the mixture is placed in a mold for shaping into the desired article, say, a grinding wheel. The mixture is molded under pressure and thus compacted to the desired degree. The resulting molded article, say, a grinding wheel blank, is then removed from the mold and dried at a temperature of, say, about 80 to 100 0., for about 4 to 5 hours to evaporate substantially completely the solvent introduced along with the phenolic resin into the blank. The blank is now ready to be vulcanized, which operation may consist in re-molding the blank under pressure for about 7 hours at a temperature corresponding to 80- pounds steam pressure. The resulting article is one wherein the resin has been further polymerized or hardened to a tough condition and wherein the rubber particles have been unified into a tough vulcanized mass serving to bond together the phenol-coated abrasive granules with high tenacity.

While various kinds of rubber in granulated or pulverulent condition may be employed in my method, I prefer to use pulverulent rubber prepared in accordance with the practice of my application Serial No. 706,858, filed January 16, 1934, nowPatent No. 2,019,055, dated October 29, 1935. Such pulverulent rubber is characterized by its derivation directly from rubber latex and, accordingly, its virgin, substantially unvulcanizcd condition. A rubber composition prepared as disclosed in that application and useful for the purpose of the present invention may comprise 100 parts of rubber to 30 to 40 parts of sulphur. It may also contain a relatively small amount of vulcanization accelerator and fillers, pigments, or other rubber-compounding agents. As further pointed out in that application, the pulverulent rubber may be derived from a substantially uncompounded rubber latex and the desired amount of sulphur, vulcanization accelerator, etc., may be mixed with the pulverulent rubber.

It is possible to deviate from the particular procedure hereinbefore outlined. Thus, the mixture prepared for molding as hereinbefore described may be initially molded and dried and the dried blank remolded at a temperature or, say, about 300 F. to cause the rubber particles to cohere. Pressure may then be exerted on the molded article to eflect the desired packing of the grain therein and to impart thereto such density as ensures a finished article of the appropriate strength and toughness. The re-molding of the blank at elevated temperature and under pressure may be carried on for a period 01' time to eiiect only partial vulcanization of the rubber, whereupon the blank may be removed from the mold and placed in a baking oven wherein it is maintained at an elevated temperature and for a period of time suflicient to complete vulcanization.

I claim:-

1. A method of making rubber-bonded abrasive products which comprises mixing as separate entities or particles abrasive grain with substantially unvulcanized pulverulent rubber, molding the mixture under pressure into a unitary mass of the desired shape, and vulcanizing the molded mass.

2. A method of making rubber-bonded abrasive products which comprises mixing as separate entities or particles abrasive grain with substantially unvulcanized pulverulent rubber as derived directly from rubber latex in the presence of added vulcanizing ingredients and molding the mixture under heat and pressure into a unitary vulcanized mass of the desired shape.

3. A method of making rubber-bonded abrasive products which comprises enveloping abrasive grain with an agent having strong bonding aflinity for both said grain and rubber, mixing the grain with substantially unvulcanized pulverulent rubber, molding the mixture into an article 01' the desired shape, and vulcanlzing the molded article.

4. A method of making rubber-bonded abrasive products which comprises wetting abrasive grain with a solution of an agent capable of hardening to a tough condition under heat and having strong bonding affinity for both said grain and rubber, mixing the grain with substantially unvulcanized pulverulent rubber in the presence or added vulcanizing ingredients, molding the mixture into an article of the desired shape, drying the article and vulcanizing it under heat and pressure.

5. A method of making rubber-bonded abrasive products which comprises wetting abrasive grain with a solution of a synthetic resin capable of polymerizing and hardening to a tough condition under heat and having strong bonding aifinity for both said grain and rubber, mixing the grain with substantially unvulcanized pulverulent rubber as derived directly from latex in the presence 0! added vulcanizing ingredients, molding the mixaosmss ture into an article or the desiredshape. drying the article, and vulcanizing it under heat and pressure.

6. An abrasive product comprising a mass of abrasive grain bonded by rubber in vulcanized condition, said grain surfaces being substantially uniformly coated with an agent having strong bonding afllnity for both said grain and rubber.

7. An abrasive product comprising a mass of abrasive grain bonded by rubber in vulcanized condition, said grain surfaces being substantially uniformly coated with a heat-polymerized agent having strong bonding aflinity for both said grain and rubber.

8. An abrasive product comprising a mas; of abrasive grain bonded by rubber in vulcanized condition, said grain surfaces being substantially uniformly coated with a heat-polymerized synties or particles abrasive particles with rubber particles capable of being caused to cohere under pressure and molding the mixture under sumcient pressure to cause said rubber particles to cohere and thus to bond the abrasive particles into a unitary mass.

10. A method of making rubber-bonded abrasive products which comprises mixing as separate entities or particles abrasive grain with 711108111! able pulverulent rubber containing added viiicanizing ingredients to produce a substantially uniform mixture and molding and vulcaniaing the mixture to form a vulcanized unitary mass of the desired shape.

ROYCE J. NOBLE. 

